1. Field of the Invention
The present invention relates to a centrifugal fan; more particularly, the present invention relates to a centrifugal fan capable of adjusting a gap size between part of a side wall and the blades.
2. Description of the Related Art
Conventionally, fans applied in computer equipment mainly comprise two types: one is an axial fan, and the other is a centrifugal fan. The major difference between the above two types of fans is the direction of outlet airflow. The outlet airflow direction of the axial fan is perpendicular to the direction of the blades, while the outlet airflow direction of the centrifugal fan is along the rotary direction of its blades. Because of the limited available space in laptop computers, most of the fans currently installed in laptop computers are centrifugal fans.
Generally speaking, a good centrifugal fan should have a high heat dissipation watts and good heat dissipation efficiency along with advantages such as low noise. Many factors, such as motor bearing selection and fan rotation speeds, can affect the generation of fan noise. It was experimentally demonstrated in 1969 that the level of the generated noise is related to the size of the gap between a tongue part and an impeller of the centrifugal fan. The experiment demonstrated that if the gap between the tongue part and the impeller is enlarged by expanding the case of a fan, narrow-band and broad-band noises can be significantly reduced.
However, enlarging the gap between the tongue part and the impeller decreases the outlet airflow of the centrifugal fan, which can result in overheating of the system due to insufficient airflow when a central processing unit or other elements of the computer are running in a high-loading operating environment. Therefore, it is important to consider both the outlet airflow of the centrifugal fan and the level of noise generated.